Oceans and Coasts

We work in India's oceanic islands and coasts with a broad mandate to understand the basic ecology and behaviour of these systems, how human communities interact with them, and the impact of disturbances — both regional and global — on this relationship.

Coral reef responses to global change

As coral reefs across the tropics succumb to increasingly frequent ocean warming events in the wake of global climate change, documenting the consequences of these events on reef communities and their ability to resist and recover from them becomes critical. Our investigations in the Lakshadweep Archipelago and the Andaman & Nicobar Islands attempt to understand the factors that confer resilience on these systems

Conflict and cooperation in the sea

Tropical coastlines are home to the highest density of people anywhere and they depend heavily on resources these waters provide. It is not unusual then that human communities interact with wild marine species that may often compete with humans for the same precious resources. We have been working to understand the interface between fishers and wild species in Indian waters, and to unpack the ecological, socio-economic and cultural drivers of these interactions

Mating successfully at high densities often requires species to employ unusual reproductive tactics. We report
unique courtship behaviours in an un shed, high-density
spawning aggregation of squaretail groupers (Plectropomus areolatus) that are potentially associated with alternative reproductive tactics (ARTs). Aggregating males are
typically known to court females in small territories (pair
courtship), which is often associated with a pair-spawning tactic. However, we also observed the largest males
simultaneously courting several females in mid-water
shoals – a unique, high-cost-high-benefit courtship tactic which appears to result in a novel school-spawning tactic. Counter-intuitively we observed an inverse size-
assortment in individuals–large males courted smaller
females and vice-a-versa, likely linked to different pay-
offs with competitive ability and local mate density. These
unique, high-density behaviours are threatened to be
lost, with increasing commercial fishing pressures on the
P. areolatus aggregation.

Human-induced rapid environmental change (HIREC) disproportionately affects species with specialist
traits and long generation times. By circumventing prolonged evolutionary processes, behavioural
plasticity is critical in allowing species to cope with rapid environmental changes within their lifetimes.
Coral reefs have faced multiple mass mortality events of corals related to climate change in the last two
decades. The consequent loss of structural complexity adversely impacts long-lived, structure-dependent
fish predators. We attempted to determine how well a guild of groupers (Pisces: Epinephelidae) copes
with rapid structural change in the lightly fished Lakshadweep Archipelago, Indian Ocean. Of the 15
species, territorial and site-attached groupers declined exponentially with decreasing structural
complexity, while widely ranging species showed no change. However, one site-attached species, the
peacock grouper, Cephalopholis argus, maintained high densities across the structural gradient. We
explored the mechanisms this species employs to cope with declining habitat structure. Our observations
indicate that both a potential release from specialist competitors and plasticity in foraging behaviour
(foraging territory size, diet and foraging mode) appeared to favour the peacock grouper's survival in
sites of high and low structure. While specialist competitors dropped out of the assemblage, the foraging
territory size of peacock groupers increased exponentially with structural decline, but remained constant
and compact (50 m2) above a threshold of structural complexity (corresponding to a canopy height of
60 cm). Interestingly, despite significant differences in prey density in sites of high and low structure, gut
content and stable isotope analyses indicated that peacock groupers maintained a specialized dietary
niche. In-water behavioural observations suggested that diet specialization was maintained by switching
foraging modes from a structure-dependent ‘ambush’ to a structure-independent ‘widely foraging’
mode. The remarkable foraging plasticity of species such as the peacock grouper will become increasingly critical in separating winners from losers and may help preserve specialist ecosystem functions as
habitats collapse as a result of climate change.

Latitude and live coral cover independently affect Chaetodontid and Pomacanthid fish community distribution in the Andaman and Nicobar archipelago, India

Empirical evidence indicates that for two reef fish groups, chaetodontids and pomacanthids, live coral cover and latitude determine the local abundance and species richness patterns. Most studies have considered the influence of either live coral cover or latitude in isolation, and the interactive effects that are likely to influence the geographical distribution of species richness and diversity has not been explored. In this study we explored the relationship between (1) species richness and latitude, and (2) species richness and benthic variables, (3) species diversity and latitude and (4) species diversity and benthic variables for butterflyfish (Chaetodontidae) and angelfish (Pomacanthidae) at 75 sites across 51 islands in the Andaman and Nicobar (A & N) archipelago. A total of 30 species of chaetodontids belonging to four genera and 13 species of pomacanthids belonging to nine genera were recorded. We found that live coral cover and latitude were the best predictors for explaining variation in the distribution of these fish communities across the A & N archipelago. This is probably because of the high dependence of these two fish groups on the live coral cover and Nicobar’s geographical proximity to the Coral Triangle, which is considered to be the centre of origin of coral reefs and supports high biodiversity. Our results show that de- spite the high dependence of chaetodontids and pomacanthids on live coral cover, reduction of live coral cover due to a series of disturbance events had limited influence on species richness of these two fish groups, indicating that broad geographical trends are important in explaining variation in species richness for chaetodontid and pomacanthid fish groups.

Increasingly frequent and intense ocean warming events seriously test the buffer and recovery capacities of tropical coral reefs. Post-disturbance, available settlement structures on a reef (often dead coral skeletons) vary considerably in their mechanical stability and substrate composition, critically influencing coral recruit settlement choice and fate. In the wake of a coral mass mortality in the Lakshadweep archipelago, we examine (1) the relative availability of recruit settlement structures (from stable to unstable: reef platform, dead massive coral, consolidated rubble, dead corymbose coral, dead tabular coral, and unconsolidated rubble) in 12 recovering reefs across three atolls in the archipelago, (2) the substrate composition [crustose coralline algae (CCA), mixed turf, macroalgae] of these structural forms, and (3) whether the choice and fate of young coral are mediated by the substrate and stability of different structural forms. For this, we measured the abundance and distribution of recruit (<1cm), juvenile (1–5 cm), and young adult (5–10) corals of 24 common coral genera. Four years after the mass mortality, reefs differed considerably in composition of settlement structures. The structures themselves varied significantly in substrate cover with dead tables largely covered in CCA [60 ± 6.05 % (SE)] and dead corymbose coral dominated by mixed turf (61.83 ± 3.8 %). The youngest visible recruits (<1 cm) clearly preferred CCA-rich structures such as dead massives and tables. However, older size classes were rarely found on unstable structures (strongly ‘‘avoiding’’ tables, Ivlev’s electivity index, E = -0.5). Our results indicate that while substrate cover might mediate coral choice, the mechanical stability of settlement structures is critical in determining post-settlement coral survival. The composition and availability of settlement structures on a reef may serve as a characteristic signature of its recovery potential, aiding in assessments of reef resilience.

Journal Article

2016

For traditional island communities in the Nicobar archipelago, complete no-go areas are the most effective form of marine managementFor traditional island communities, no-go areas are the most effective form of management

For traditional island communities in the Nicobar archipelago, complete no-go areas are the most effective form of marine management

The ability of local communities to sustainably manage natural resource harvests in coral reefs ecosystem
depends heavily on the strength of traditional institutions. Coastal communities have evolved a suite of
restrictive practices to control marine offtake and there is considerable recent evidence of their effec-
tiveness in protecting and enhancing resource stocks. However, traditionally imposed restrictions can
vary considerably in their complexity and in their functional effectiveness. The indigenous communities
of the Nicobar Islands are dependent on marine resources for sustenance, managing them with a range of
traditionally imposed restrictions. These include limited entry to certain locations, closed seasons and
areas, and restrictions on species, size-classes of fish and fishing methods. We tested the relative
effectiveness of protection in areas managed under different traditional control regimes by comparing
the abundance and biomass of targeted fish groups in managed and unmanaged areas. Our results
indicate that reef sites with the strictest form of restriction e essentially no-go areas e had significantly
higher abundance and biomass values of most functional groups of fishes compared with partially
protected and control locations. In contrast, targeted food fish stocks did not differ from control locations
in partially protected sites managed with even complex forms of traditional management. Ensuring that
traditional harvest rules are complied is critical to the success of any management system, and our re-
sults suggest that they can be most strictly enforced in traditional no-go areas. Our work highlights the
importance of critically evaluating the factors influencing traditional management systems to strengthen
their ability to protect these reefs from unsustainable overharvest.

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